1. Field of the Invention
This invention relates to locksmith apparatus and, more particularly, to locksmith apparatus for determining the length of lock pins for expediting the cutting of keys when a key to be duplicated is not available.
2. Description of the Prior Art
In the prior art, there are generally two ways of making keys for conventional locks. The first way is to simply duplicate a known key. That is, a key is known to work in a given lock, and the same type of a duplicate key is made from that key. Key cutting equipment designed to follow the configuration of an existing key is well known and understood. Thus, the key to be duplicated is secured in the key cutting apparatus, and by following the contours of the known key, a duplicate key is cut from a blank.
The second way of making a key is to know the "number" of a given key. The "number" of the key is a code indicating the length of the pins or lock elements in the lock. Knowing the number of a particular key, another key may be made by duplicating the length of the lock elements in terms of the depth of cuts on the key blank which correspond to the number of the lock.
For pin type locks, there are generally five or six pins or pin tumblers in discrete cylinders within a lock housing and within a rotatable lock cylinder or plug. There may be more pins, also, in some locks. The lengths of the pins vary. It is the variable length of the pins that determines the "number" of the lock. Since there are ten different lengths of pins, ranging in number from zero to nine, the "number" of a particular lock will have numbers in sequence which correspond to or which represent the lengths of the tumbler pins. The quantity of numbers will correspond to the quantitative number of discrete cylinders which receive the pins or tumbler pins. A locksmith will accordingly know the length of each pin by knowing the number of each pin and the sequence in which the numbers fall. The length of the pins varies inversely with the number. Thus, the number "0" pin is the longest, and the number "9" pin is the shortest.
As an example of lock numbering, a particular key may be numbered 20579. The "2" indicates that the first pin is a number 2 pin, which is of a particular length. The first cut on the key will correspond to the length of a number 2 pin. The "0" indicates that the next pin is a number 0 pin, which is the longest pin, and the corresponding cut on a key will be very shallow. The third number, the "5" in the key number, indicates that the third pin is a number 5 pin, and the depth of the cut will be about half way between the minimum depth of a zero cut and the maximum depth of a nine cut. The "7" indicates that the fourth pin is a number 7 pin, which is a relatively short pin. Finally, the "9" in the number indicates that the fifth pin is a number "9" pin, which is the shortest pin, and the depth of the cut in a key blank will be maximum depth.
There are individual or discrete cylinders within a lock housing which are aligned with discrete cylinders in the rotating cylinder or plug portion of the lock. Within the lock housing and within the cylinders are compression springs and driver pins. The housing cylinders and driver pins are of predetermined length, and each of the upper or driver pins is the same length. The compression springs bias the driver pins against the pin tumblers or lower pins. The compression springs will compress to a minimum, known length.
The lower pins or tumbler pins extend downwardly or outwardly under the bias of the compression springs and the upper or driver pins. They rest on what is referred to as the main key cut in the key way of the rotating cylindrical portion of a lock. When a key is inserted into a lock, the pin tumblers are biased upwardly or outwardly by the key. To enable a lock to be unlocked, the upper portion of each lower pin must be at the top or upper portion of the rotating cylinder, and the bottom portion of the driver pins must also be at that same location. The location is known as the shear point or break point of the lock.
If a key extends into a key way and does not bias the lower pins to the shear point, the lock cylinder will not rotate, and the lock will not unlock, or lock, whichever may be the case. However, when a key is extended into a key way which has the cuts on it corresponding, in depth, to the length of the various lower pins, the lower pins are raised to the shear point, and the rotating lock cylinder will accordingly rotate. If just one key cut is wrong, the lock cylinder will not rotate. Thus, all of the cuts on the key must be correct.
For any given lock, the distance between the main key cut and the top of the rotating lock cylinder is known, and the length or depth of each cylinder in the housing is also known. In addition, the length of the compression spring at maximum compression is known, and the length of each upper or driver pin is also known. By raising each lower pin so that the compression spring is compressed to its minimum length, and by measuring the distance each lower pin or tumbler pin moves during the compression of each spring, relatively simple mathematical calculations will give the length of each lower pin. The length of the lower pins is then correlated against a table which gives the pin numbers in terms of pin lengths. Thus, the "number" of a lock may be determined and a key may be made when the number of each pin is known.
Moreover, by compressing all springs, and by then allowing the springs to expand a known distance equal to the length of the discrete cylinders in a lock housing less the known length of the driver pins, the driver pins and lower pins will be at the shear point and the lock cylinder may then be rotated.